Question 1

Which of the following best describes the main difference between a genetic map and a physical map of a chromosome?

Accepted Answer

A genetic map is based on the frequency of recombination between genetic markers, while a physical map is based on the actual DNA sequence and distances measured in base pairs.

Question 2

A researcher is mapping a gene using recombination frequencies and observes that the calculated genetic distance underestimates the actual physical distance. What is the most likely explanation for this observation?

Accepted Answer

Double and triple crossovers between gene markers can occur, which are not detected by recombination frequency calculations.

Question 3

Which of the following statements about single nucleotide polymorphisms (SNPs) is correct?

Accepted Answer

SNPs are single base pair changes present in at least 1% of the population and are responsible for most genetic variation between individuals.

Question 4

A patient is tested for a disease-associated SNP using RFLP analysis. The disease allele removes a restriction site for EcoRI. After digestion and gel electrophoresis, which pattern would indicate the patient is homozygous for the disease allele?

Accepted Answer

A single larger DNA fragment is observed, as EcoRI cannot cut at the mutated site.

Question 5

Which of the following best explains why RFLP analysis can be used to distinguish between taster and non-taster alleles of the TAS2R38 gene?

Accepted Answer

A SNP in the gene creates or abolishes a restriction enzyme recognition site, resulting in different fragment sizes after digestion.

Question 6

A Southern blot is performed after digesting DNA with a restriction enzyme. The probe hybridizes to a 5 kb fragment in the normal allele and a 2 kb fragment in the mutant allele. What is the genotype of an individual who shows both 5 kb and 2 kb bands?

Accepted Answer

Heterozygous (one normal and one mutant allele)

Question 7

Which of the following is a key technical requirement for performing PCR-based RFLP analysis?

Accepted Answer

DNA primers specific to the region of interest

Question 8

A DNA sample is digested with HaeIII and analyzed by gel electrophoresis. The taster allele of TAS2R38 produces two fragments (177 bp and 44 bp), while the non-taster allele produces one fragment (221 bp). What banding pattern would you expect for a heterozygous individual?

Accepted Answer

Bands at 221 bp, 177 bp, and 44 bp

Question 9

Which of the following best describes the role of a DNA probe in Southern blotting?

Accepted Answer

It hybridizes to a specific DNA sequence of interest, allowing detection of fragments containing that sequence.

Question 10

A family pedigree shows an autosomal recessive disease. RFLP analysis reveals that the disease allele is always associated with a 2 kb fragment, while the normal allele is associated with a 5 kb fragment. Which genotype would be expected for an affected individual?

Accepted Answer

Homozygous for the 2 kb fragment

Question 11

Which of the following is a limitation of using recombination frequency to estimate genetic distance?

Accepted Answer

Double crossovers can occur, leading to underestimation of the true distance.

Question 12

A lactose gene is analyzed by PCR and digested with BglII. The tolerant allele produces fragments of 1000 bp, 600 bp, and 200 bp, while the intolerant allele produces fragments of 1000 bp and 800 bp. What banding pattern would you expect for a lactose intolerant homozygote?

Accepted Answer

Bands at 1000 bp and 800 bp

Question 13

Which of the following best explains why some regions of the genome are 'hot spots' for recombination?

Accepted Answer

The probability of crossover is not uniform along the chromosome, and certain regions have higher recombination rates for reasons not fully understood.

Question 14

A Southern blot is performed on DNA from individuals with an X-linked recessive disorder. The mutant allele removes an EcoRI site, resulting in an 8 kb fragment, while the normal allele produces 5 kb and 3 kb fragments. What pattern would you expect for a female carrier?

Accepted Answer

Bands at 8 kb, 5 kb, and 3 kb

Question 15

Which of the following is NOT a possible consequence of a single nucleotide polymorphism (SNP) within a gene?

Accepted Answer

It always results in a nonfunctional protein.

Question 16

In a population, a SNP is found at position 145 of the TAS2R38 gene. The taster allele encodes Proline (Pro), while the non-taster allele encodes Alanine (Ala). Which molecular technique would best distinguish between these alleles?

Accepted Answer

RFLP analysis using a restriction enzyme that recognizes the sequence altered by the SNP

Question 17

Which of the following equations correctly describes the exponential amplification of DNA during PCR, where $$n is $$the number of cycles?

Accepted Answer

$$2^n$$

Question 18

A patient’s DNA is analyzed for a disease-causing mutation using RFLP and Southern blotting. The probe hybridizes to a 2 kb fragment in the mutant allele and a 5 kb fragment in the normal allele. If the patient is homozygous for the mutant allele, what will be observed on the blot?

Accepted Answer

Only a 2 kb band will be present.

Genomic Mapping and Polymorphism Analysis in Human Genetics

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